Messages in this thread Patch in this message | | | Subject | Re: ext2 + -osync: not as easy as it seems | From | Fernando Luis Vázquez Cao <> | Date | Thu, 15 Jan 2009 21:06:51 +0900 |
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On Wed, 2009-01-14 at 11:59 -0500, Theodore Tso wrote: > On Wed, Jan 14, 2009 at 03:37:56PM +0100, Jan Kara wrote: > > > Um, we have that already; the sync_inode() followed by > > > blkdev_issue_flush() is the path taken by fdatasync(), I do believe. > > > > Maybe ext4-patch-queue changes that area but in Linus's tree I see: > > > > if (datasync && !(inode->i_state & I_DIRTY_DATASYNC)) > > goto out; > > > > So if we just overwrite some data, we send them to disk via fdatawrite() > > and then we quickly bail out from ext4_sync_file() without doing > > blkdev_issue_flush(). > > So you're thinking about fdatawrite() being called by some code path > other than ext4_sync_file() before we call fsync()? Yeah, that could > happen.... I think that will only happen if the file is opened > O_SYNC, but that raises another issue, which is that we're not forcing > a flush for writes when the file is opened O_SYNC.
Hi Jan, Ted
Is something like the patch below what you had in mind?
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From: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp> Subject: ext3: call blkdev_issue_flush on fsync
To ensure that bits are truly on-disk after an fsync or fdatasync, we should call blkdev_issue_flush if barriers are supported.
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp> ---
--- linux-2.6.29-rc1-orig/fs/ext4/fsync.c 2008-12-25 08:26:37.000000000 +0900 +++ linux-2.6.29-rc1/fs/ext4/fsync.c 2009-01-15 21:03:19.000000000 +0900 @@ -48,6 +48,7 @@ int ext4_sync_file(struct file *file, st { struct inode *inode = dentry->d_inode; journal_t *journal = EXT4_SB(inode->i_sb)->s_journal; + unsigned long i_state = inode->i_state; int ret = 0; J_ASSERT(ext4_journal_current_handle() == NULL); @@ -79,22 +80,35 @@ int ext4_sync_file(struct file *file, st goto out; } - if (datasync && !(inode->i_state & I_DIRTY_DATASYNC)) - goto out; + if (datasync && !(i_state & I_DIRTY_DATASYNC)) + goto flush_blkdev; /* * The VFS has written the file data. If the inode is unaltered * then we need not start a commit. */ - if (inode->i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC)) { + if (i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC)) { struct writeback_control wbc = { .sync_mode = WB_SYNC_ALL, .nr_to_write = 0, /* sys_fsync did this */ }; ret = sync_inode(inode, &wbc); - if (journal && (journal->j_flags & JBD2_BARRIER)) - blkdev_issue_flush(inode->i_sb->s_bdev, NULL); + /* + * When there are no blocks attached to the journal transaction + * some optimizations are possible, but if there were dirty + * pages sync_inode() should have ensured that all data gets + * actually written to disk. Thus, we can skip + * blkdev_issue_flush() below. + */ + if (!(i_state & I_DIRTY_PAGES)) + goto flush_blkdev; } + + goto out; + +flush_blkdev: + if (journal && (journal->j_flags & JBD2_BARRIER)) + blkdev_issue_flush(inode->i_sb->s_bdev, NULL); out: return ret; }
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